FEN: Hyponatremia and Hypo-osmolal States Flashcards
1
Q
Describe laboratory values and steps in diagnosis of hyponatremia
A
- Measure [serum sodium]
- Measure [serum osmolality] to determine if hyperosmotic, iso-osmotic or hypo-osmotic hyponatremia
- If hypo-osmotic, measure [urine osmolality] (measure body response to hyponatremia)
- Measure [urinary sodium] to assess water retention/sodium retention mechanisms
2
Q
A serum sodium less than what ? mEq/L usually correlates with a reduction in plasma osmolality?
A
Na+ less than 136 mEq/L
3
Q
Describe the fluid shift that occurs with hyponatremia and subsequent hypo-osmolality
A
Fluid shift into cells resulting in cellular overhydration
4
Q
Dx with low plasma sodium and normal plasma osmolality
A
Pseudohyponatremia
- Hyperlipidemia (can also be elevated osmolality in severe)
- Hyperproteinemia
5
Q
Dx with low plasma sodium and elevated plasma osmolality
A
Pseudohyponatremia
- Hyperglycemia
- Mannitol
6
Q
What is pseudohyponatremia?
A
Although plasma Na+ is low, total body Na+ content is normal. Instead, the body is adapting to increased osmolality:
- Na+ shifts into cells
- Water shifts from inside cells to EC compartment, diluting Na+ concentration.
7
Q
Explain how urine osmolality is used in differential diagnosis of hyponatremia
A
- Hypervolemia vs. Hypo or Eu-volemia is often easy to make based on physical exam and history
- Hypo- vs. Euvolemia is more difficult.
- The body’s normal response to hyponatremia (low serum osmolality) is suppress ADH and to excrete maximally diluted urine, i.e. Urine osm less than 100 mOsm/kg
- Urine osmolality greater than 100 mOsm/kg indicates body cannot excrete dilute urine
- This is often a result of SIADH, such as due to medications.
8
Q
Describe the pathophysiology of Heart Failure and Hyponatremia
A
- In heart failure, there is a reduction in effective circulatory blood volume
- This decrease in cardiac output and weakening of sensitivity of baroreceptors provides
- A non-osmotic release of arginine vasopressin
- This reduces the ability of the kidneys to dilute urine in setting of hypoosmolar hyponatremia.
9
Q
Describe the pathophysiology of cirrhosis and nephrotic syndrome in hyponatremia
A
- Nephrotic syndrome is a kidney disorder that causes body to pass too much protein in urine, resulting in a urine that is not maximally dilute (impaired water excretion).
- Cirrhosis results in portal hypertension and associated systemic vasodilation, which causes decrease in effective circulatory blood volume. This causes non-osmotic release of ADH.
10
Q
Describe hypovolemic hyponatremia
A
Deficit of both Na+ and fluid, but total Na+ is decreased more than total body water
11
Q
Describe euvolemic hyponatremia
A
Normal total body Na+ with excess fluid volume (i.e. dilutional)
12
Q
Describe hypervolemic hyponatremia
A
Excess Na+ and fluid, but fluid excess predominates
13
Q
Give four examples of hypovolemic hyponatremia
A
- fluid loss (e.g. emesis, diarrhea, fever)
- Third spacing
- Renal loss (diuretics)
- Cerebral salt wasting
14
Q
Give two examples of euvolemic hyponatremia
A
- SIADH
2. Drug-induced SIADH
15
Q
Give two examples of hypervolemic hyponatremia
A
- Edematous disorders (HF, cirrhosis, nephrotic syndrome)
2. Acute or ochronic renal failure
16
Q
How can you use urinary sodium and urine osmolality in differential diagnosis of HYPOvolemic hyponatremia?
A
- Urine sodium less than 25 mEq/L indicates nonrenal loss (e.g. fluid loss, cerebral salt wasting, third spacing)
- Urine sodium greater than 40 mEq/L indicates renal loss of Na+ (e.g. diuretics)
17
Q
How can you use urinary sodium and urine osmolality in differential diagnosis of HYPERvolemic hyponatremia?
A
- Urinary sodium less than 25 mEq/L indicates edematous disorders (HF, cirrhosis, nephrotic syndrome)
- Urine sodium greater than 25 mEq/L indicates acute or chronic renal failure
18
Q
Three ways volume status can be assessed in setting of hyponatremia?
A
- Skin turgor
- Jugular venous pressure
- urine sodium
19
Q
Describe the water content of the body in SIADH
A
- Although SIADH is considered a “euvolemic hyponatremia”
- This is because extracellular (interstitial and intravascular) compartments are near normal, however, intracellular is above normal.
- In the acute state of SIADH, hypervolemia caused by inability to concentrate urine results in natriuresis
- At steady state, urine sodium matches sodium intake, which explains urine sodium being greater than 40 mEq/L.
20
Q
What are diagnostic laboratory parameters for SIADH?
A
- Low serum sodium
- Urine osmolality greater than 100 mOsm/kg (reflecting inability to excrete free water)
- Urine sodium greater than 40 mEq/L (reflecting natriuresis to compensate for inappropriate ADH)
- Should also consider normal thyroid, normal cortisol, absence of kidney/heart/liver problems.
21
Q
List five common causes of hyponatremia
A
- Replacement of lost solute with water
- Volume depletion and organ hypoperfusion
- SIADH, endocrine disorders
- Drug-induced
- Renal failure
22
Q
Describe how replacement of lost solute with water causes hyponatremia
A
- Loss of solute (e.g. vomiting, diarrhea) usually involves loss of isotonic fluid, therefore, alone it will not cause hyponatremia
- After the loss of isotonic fluid, hyponatremia can develop when the lost fluid is replaced with water (i.e. enteral free water)
- A common cause of hyponatremia in hospitals is the postoperative administration of hypotonic fluid
23
Q
Describe how volume depletion and organ hypoperfusion causes hyponatremia
A
- Both volume depletion and organ hypoperfusion (i.e. heart failure, cirrhosis) cause decreased effective circulating volume,
- Baroreceptors overpower osmoreceptors causing non-osmotic release of ADH
- This reduces ability of kidneys to dilute urine despite hypo-osmolar state.
24
Q
List six etiologies of SIADH
A
- Central nervous system disturbances (stroke, infection, trauma, hemorrhage, psychosis)
- Malignancies (tumors can produce ectopically & some chemotherapies and targeted cancer treatments cause SIADH)
- Pulmonary disease (pneumonia, asthma, acute respiratory failure, atelectasis, pneumothorax)
- Surgery
- Vasopressin, desmopressin, oxytocin administration
- Hereditary SIADH
- HIV infection and AIDS
25
List two common endocrine disturbances that can cause hyponatremia similar to SIADH
1. Cortisol (adrenal) deficiency
| 2. Hypothyroidism
26
List six most drug classes and drugs which cause SIADH (Hint: 1 cardiac, three psychotropic, 1 analgesic and cancer)
1. Diuretics (thiazide and loop)
2. Antidepressants (especially SSRI** and SNRI and Tricyclic*)
3. Antipsychotics (esp. Haloperidol)
4. Antiepileptics, especially carbamazepine and oxcarbazepine)
5. NSAIDs
6. Anticancer agents (vinca alkaloids, platinum, alkylating agents [cyclophosphamide, melphalan, ifosfamide], other miscellaneous)
27
What are two risk factors for drug-induced SIADH?
1. Older adults
| 2. Those who drink large volumes of water
28
Describe how renal failure contributes to hyponatremia
Renal failure impairs the ability to excrete dilute urine, predisposing to hyponatremia
29
What phenomenon is attributed with causing symptoms of hyponatremia?
Hyponatremia causes hypo-osmolality, with subsequent water movement into brain cells causing cerebral edema
30
Over what time frame of development is acute hyponatremia?
1-3 days
31
What two numbers predict the neurologic symptoms of hyponatremia?
1. Rate of change in serum sodium
| 2. Degree of change in serum sodium
32
Why might patients with chronic hyponatremia show less severe or no symptoms?
1. Osmotic adaptation occurs
| 2. Solutes move out of brain cells to prevent osmotic shift of water into brain cells, reducing cerebral cell swelling
33
The hyponatremia symptoms of nausea and malaise are characteristic of what serum sodium level?
120-125
34
The hyponatremia symptoms of headache, lethargy, obtundation, unsteadiness, confusion are characteristic of what serum sodium level?
115-120
35
The hyponatremia symptoms of delirium, seizure, coma, respiratory arrest, death are characteristic of what serum sodium level?
less than 115
36
List four principles of treating hyponatremia
1. Treat underlying cause (endocrine, drug-induced, etc.)
2. Correct Na+ at no greater than 10-12 mEq/L in 24 hours.
3. Treatment depends on volume status, symptom severity, and hyponatremia onset.
4. Correct hyperkalemia if present
37
List three hyponatremia treatment options for patients with euvolemic or hypervolemic hyponatremia
1. Fluid restriction (first line)
2. Vasopressin antagonists
3. Hypertonic saline (ONLY if symptomatic, and will likely need diuretics to manage volume)
38
How to do fluid restriction for asymptomatic hyponatremia?
Less than 800 ml/day
39
What are two vasopressin antagonists and describe their benefits and lack of benefits in euvolemic and hyperovlemic patients
1. IV conivaptan, PO tolvaptan
2. Promotes aquaresis, increases serum sodium, alleviates symptoms, reduces weight
3. Does NOT decrease fall prevention, hospitalization, hospital length of stay, quality of life or mortality.
40
List four clinical pearls for using vasopressin antagonists in hyponatremia
1. 3A4 substrates and inhibitors: monitor for drug interactions that could increase effect, causing rapid serum sodium increase
2. Fluid restriction within first 24 hours can increase risk of rapid correction (can start after 24 hours)
3. Tolvaptan should not be administered more than 30 days to minimize liver injury risk
4. Monitor for recurrence of hyponatremia once treatment is stopped.
41
What is the first step in treating hypovolemic hyponatremia, and why?
1. Volume resuscitation
2. Until volume is restored, patient will continue to secrete ADH, causing water reasbroption and subsequent hyponatremia.
42
Why is careful monitoring necessary when doing volume resuscitation in patients with hypovolemic hyponatremia?
1. Once intravascular volume is restored, ADH secretion will decrease
2. Causing free water to be excreted. This can lead to a rapid correction in serum sodium.
43
List three etiologies of hypovolemic hyponatremia that may require additional Na+ after intravascular volume is restored
1. Volume depletion
2. Diuretic-induced
3. Adrenal insufficiency
44
What equation can be used to estimate sodium deficient in hyponatremia?
Total body Sodium deficient = total body water * (desired serum Na - Pt serum Na)
Total body water can be estimated as LBW * 0.6 in males and 0.5 in females.
45
What equation can be used to estimate hypertonic saline 3%
Estimate an infusion rate of 3% hypertonic saline by multiplaying ideal body weight (IBW) by desired rate of serum sodium increase per hour
*Infusion rate is typically 0.5-2 mL/kg/hour
46
If calculating the sodium deficient, how much of deficiet should be replaced in the first 24 hours?
25-50% of the deficient, not to exceed 10-12 mEq/L/24 hours.
47
Regardless of method used to estimate Na+ replacement, what type of monitoring and adjustments need to occur?
1. The amount of Na+ administered needs to be adjusted
| 2. Based on serial serum sodium concentrations (e.g. every 4 hours).
48
What treatment options needs to be considered for all patients with symptomatic hyponatremia?
Hypertonic saline
49
Why must caution be given when correcting hypokalemia in the presence of hyponatremia?
1. Hypokalemia will cause a reduction in serum sodium because Na+ enters cells to account for reduction in IC K+ to maintain cellular electroneutrality
2. Administration of K+ will correct hyponatremia
3. Administering K+ may cause overly rapid correction of serum sodium, irrespective of sodium being administered.
50
What treatment can be given to patients with cerebral salt wasting to prevent hyponatremia?
Sodium chloride tablets or flurdorcortisone
51
List three types of drugs that can be used in patients with euvolemic hyponatremia to promote aqueresis
1. Demeclocycline
2. Vasopressin antagonists
3. Urea
